1 Samuel 17:39-40

39And David girded his sword upon his armour, and he tried to go; for he had not proved it . And David said to Saul, I cannot go with these; for I have not proved them . And David put them off from him.

40And he took his staff in his hand, and chose for himself five smooth stones out of the brook, and put them in a shepherd’s bag which he had, even in a bag; and his sling was in his hand: and he drew near to the Philistine.12